Water Utilities Are Starting to Take Their Own Conservation Advice

Wastewater treatment plants are often the biggest consumers of electricity in their areas. Gresham, Ore., and Washington, D.C., are making moves to change that.

D.C. Water is adopting Norway's Cambi system at its advanced waste treatment plant, heating waste to create and capture methane that's then burned to generate electricity. These stainless steel vessels heat the sludge to 320 degrees before moving it to four large concrete tanks called anaerobic digesters. (Photos by David Kidd)

To inspect the anaerobic digesters, workers must use ladders to climb in and out of the tanks. The technology D.C. Water is using is called thermal hydrolysis. Once the system is completed, it will be the largest thermal hydrolysis plant in the world.

Chris Peot, director of resource recovery at D.C. Water, climbs into one of the digesters. The tanks are about 75 feet tall and 100 feet in diameter.

These vast, domed tanks will eventually be filled with the District's waste. The blue vertical tubes suck the sludge from the bottom and spits it back out near the top. The sludge will stew in these tanks for about two weeks, producing methane that vents out a pipe at the dome.

The steel centrifuges drain any liquid from the waste as it first enters the process. From here, the sludge flows into the two-dozen stainless steel tanks.

Construction is still ongoing at the waste treatment plant. D.C. Water expects the plant to be fully operational by 2015.

The $460-million project is part of a culture of innovation at the agency. D.C. Water has also pursued groundbreaking customer solutions to generate more precise meter readings and is planning on issuing the first municipal "century bond" this year.

D.C. Water is the local electricity company's No. 1 customer. But once completed, the thermal hydrolysis process will cut the agency's electricity bill by about one-third or $10 million a year.

One of the four anaerobic digesters.

The view from the top of a digester tank.

An overview of the sedimentation basins at the plant. Part of the liquid side of the waste treatment process, these basins separate out the solids containing carbon and nutrients.

The methane generated from the digesters fires three jet turbine engines and produces electricity. A byproduct of that process is steam, which is fed back into the plant.

Water utilities are huge energy hogs. That shouldn’t be surprising: Producing and transporting clean water require enormous amounts of energy, as does processing wastewater. In fact in most cities, water agencies are electric companies’ No. 1 customers.

That’s true in Gresham, Ore., and Washington, D.C. That status, though, is about to change: Both cities have embarked on major projects at their wastewater treatment plants that will produce on site just about all the energy consumed at these facilities. It’s a sign of the times. Between severe droughts in much of the country and strained operating budgets, more and more utilities are recognizing the need to conserve.

For the city of Gresham, the impetus was its mayor’s energy management program. Mayor Shane Bemis believed the fastest way to reach the city’s energy reduction goals was to target its top energy users. So the Gresham Wastewater Treatment Plant, a 20-million-gallon-per-day facility that serves 108,000 customers, set an ambitious goal: It would produce 100 percent of its electricity needs from on-site renewable power by the end of 2014.

Gresham is well on its way to meeting its target. Through a combination of cogeneration and solar power, the wastewater treatment plant is currently producing about 60 percent of the energy it uses. Its cogeneration engine works by capturing the methane gas produced from the plant’s digesters -- where the waste is processed -- and turning it into electrical power and heat. This has reduced the city’s annual electricity costs by $260,000. The cogenerator produces 50 percent of the plant’s energy, and its solar arrays, one of the largest land-based installations in the Northwest, produce 7 percent. That, along with about 18 percent of renewable energy purchased from the electric company, makes the plant about 75 percent sustainable. To reach its 100 percent goal, the city wants to double its cogeneration capacity and is currently implementing a program to generate energy from grease waste. All of these efforts are part of a seven-year, $21 million contract with the firm Veolia Water.

Similarly, D.C. Water is set to produce 13 megawatts of power -- about one-third of the energy the facility consumes -- through a process called thermal hydrolysis. It’s a technique that is already in use in Europe but is about to be employed in North America for the first time. As in Gresham, the goal is to use the methane produced to generate electric power. Here’s how it works: Waste flows into stainless steel vessels called Cambis, named for the Norwegian company that builds them. The waste, or “enriched water,” as D.C. Water General Manager George Hawkins calls it, is heated to more than 320 degrees under more than 130 pounds of pressure. It is eventually moved to four large anaerobic digesters,

where the methane gas is produced. Once the more than $400-million system is in full service -- D.C. Water begins testing this month -- it will be the largest clean energy source in the Mid-Atlantic at a treatment facility, says Hawkins. It will cut D.C. Water’s electricity bill by about $10 million a year.

Both projects were motivated, according to Bemis and Hawkins, as much by cost savings as the growing need to be energy efficient. “It could be a game changer for energy,” Hawkins told The Washington Post. “If we turn every enriched-water facility in the United States into a power plant, it would become one of the largest sectors of clean energy that, at the moment, is relatively untapped.”